Method and apparatus for making glass windshields

ABSTRACT

Windshields are made from vertically drawn glass in accordance with a method that involves scanning substantially the entire width of the glass with a distortion-analyzer apparatus that produces a trace or other record proportional to the second derivative with respect to distance traversed of the thickness of the glass, and then cutting from the glass so scanned at least one piece of windshield blank, with the windshield blank being taken from a portion of the piece wherein said derivative is at a minimal value.

ll "l4 n 1 l Poola 5] Feb, 11 M72 [54] METH'UD AND APPARATUS FOR3,216,809 11/1965 Slabodsky ..65/29 MAKllNG GLASS WINDSHIELDS 3,535,522/1970 Green ..65/29 UX [72] Inventor: .lngadeesan V. Pools, Bridgeport,W. Va. Primary Examiner keuben Friedman [73] Assignee: PPG Industries,Inc., Pittsburgh, Pa. Assistant Examiner-Saul R. Friedman [22] Filed:Jan. 16 1970 Attorney-Chisholm and Spencer [21] Appl. No.: 3,38% [57]ABSTRACT Windshields are made from vertically drawn glass in ac- [52]US. Cl ..65/29, /97, 65/158, cordance with a method that involvesscanning substantially 234/3, 356/120, 356/239 the entire width of theglass with a distortion-analyzer ap- "gs ggfiqb s l l z 8 paratus thatproduces a trace or other record proportional to o i i i the secondderivative with respect to distance traversed of the 234/3; 83/7 56;356/ 239i250/833 thickness of the glass, and then cutting from the glassso Ref r Ct d scanned at least one piece of windshield blank, with the ewees le windshield blank being taken from a portion of the piece UNITEDSTATES PATENTS wherein said derivative iS at a minimal value.

2,452,364 10/ 1948 Fowler et a1. ..65/29 UX 4 Claims, 5 Drawing Figures2. FLAPPINO 261 EQUIPMENT CUTT'NG 3o ecu "mam r 32 G 36 1 :uomr souacemm m 1197: $639.1. 12

n/\ \J N0 Wmmsmm @LANK Efi A (7 m 22 5 M W A U V E WINUEHIELD BLANK,

2% g wwm @m-wm DRAW MMHINE 2 INVENTOR ATTORNEYS TWQ WINDSHIELD @LANMS VMETHOD AND APPARATUS FOR MAKING GLASS WINDSHIELDS BACKGROUND OF THEINVENTION This invention relates to the making of automotive windshieldsfrom vertically drawn glass.

DESCRIPTION OF THE PRIOR ART Prior to the present invention, automotiveWindshields and the like have not been made from vertically drawn glass,chiefly because of the problems involved in arriving at product ofsuitable low-distortion characteristics. Instead, windshields have beenmade of float glass or plate glass, two panes of such glass beingpressed together with a suitable plastic interlayer to form the productwindshield.

In testing flat glass for low-distortion characteristics, one known testis the Disappearance Test, such as that disclosed in James and Ward US.Pat. No. 3,097,942. Although this test is adequate to give an indicationof improvement in the quality of vertically drawn sheet glass so long asthe glass is of relatively low quality, the test tends to becomeinaccurate before the glass is so good in freedom from distortion as tobecome com mercially acceptable for use in making Windshields.

It is known, for example, from the copending application of Roy W.Yunker et al., Ser. No. 3,382 now abandoned filed of even date herewith,to construct and use a distortion-analyzer machine that produces an X-Ytrace indicative of the second derivative of the thickness of the glassscanned by the machine. Said second derivative is, as taught in thatcopending application, closely related to the low-distortioncharacteristics of the glass.

SUMMARY OF THE INVENTION Windshields are made from vertically drawnglass in accordance with a method that involves scanning substantiallythe entire width of the glass with a distortion-analyzer apparatus thatproduces a trace proportional to the second derivative with respect todistance traversed of the thickness of the glass, and then cutting fromthe glass so scanned at least one piece of windshield blank, with thewindshield blank being taken from a portion of the piece wherein saidderivative is at a minimal value.

DESCRIPTION OF THE DRAWINGS A complete understanding of the inventionmay be had from the foregoing following description thereof, takentogether with the appended drawings, in which:

FIG. 1 is a distortion-analyzer trace substantially across the entirewidth of the sheet of glass, the piece of glass being of such quality asto yield one windshield;

FIG. 2 is a distortion-analyzer trace substantially across the entirewidth of the sheet of glass, the piece of glass being of such quality soas to yield no Windshields;

FIG. 3 is a distortion-analyzer trace substantially across the entirewidth of the sheet of glass, the piece of glass being of such quality soas to yield two Windshields;

FIG. 4 is a distortion-analyzer trace substantially across the entirewidth of the sheet of glass, the piece of glass being of such quality soas to yield one windshield, taken from a particular location across thewidth of the sheet;

FIG. 5 is a schematic diagram of the apparatus of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the production of sheetglass by a vertical drawing process, it is quite possible that someportions of the sheet will not exhibit the low-distortioncharacteristics that are required for windshield blanks, and thoseportions will need to be diverted to other uses or discarded. Forexample, let us assume that we have a ribbon nominally 100 inches wide,and we edge-trim 5 inches from each edge. That leaves a width of 90inches, and it is quite possible that there will be saved from such anedge-trimmed sheet, inches wide by 70 inches long, only one windshieldblank, roughly 32 inches by 70 inches, corresponding to the best 32-inchsection across the width of the sheet. To be surest of obtaining awindshield blank of high quality, the windshield blank is preferably cutso that its length is parallel to the length of the ribbon as it emergesfrom the drawing machine. When the process is operating slightly better,it is possible that there will be two such low-distortion sectionsacross the width of the sheet, so that from a 70-inch length, twoWindshields will be saved. When the process is operating ideally so thatthe product is of exceptional quality throughout a large portion of thewidth of the ribbon, it will prove possible and desirable to cut thewindshield blank the other way, i.e., so that its length runs across theribbon rather than along it. This gives a remarkably better yield, butit is not always possible to obtain. In trying to produce sheet glass ofremarkable low-distortion characteristics on a substantial scale, thereare so many things that may change, having a consequent effect upon thequality of the portion of the sheet of glass being produced across itswidth, that it is usually necessary to count upon cutting windshieldblanks from the sheet so that they run along the length of the ribbon.

In the absence of having sophisticated equipment for determining thequality of the glass sheet as respects its low-distor tioncharacteristics, it is possible, for example, to take glass sheets 90inches wide and 70 inches long and position them, held at a suitableangle, between a light source and a wall or screen, observing then theshadow produced on the wall or screen and determining from that whetherto save from the sheet zero or one or two Windshields. This practice istimeconsuming, cumbersome, and not especially accurate. Because of thecumbersomeness of this practice, only a relatively small percentage ofthe blanks can be tested, with it ordinarily being necessary to test oneand then to cut it and the next several or few dozen pieces the sameway. This makes it difficult to control the quality of the product sothat the proportion of rejected windshield blanks remain satisfactorilylow.

Fortunately, there has been developed a distortion-analyzer apparatusthat has hitherto been used for monitoring or determining the distortionquality of flat glass, and in particular of plate glass and float glasshitherto used for making Windshields. The distortion-analyzer equipmentis more fully described in the copending application of Roy W. Yunker etal., Ser. No. 3,382 now abandoned, filed of even date herewith. Themachine yields, on an XY recorder, a trace of the second derivative ofthe thickness of the glass with respect to time or, what is the samething if a constant traverse rate is used with respect to distancetraversed, as determined by passing a sample of glass between acollimated source of visible light and a masked sensor, as described inthe above-mentioned application, which is herein incorporated byreference. The equipment is such as to be sensitive to variations inapparent power magnification on the order of 0.005 diopter. An apparentpower of magnification of 0.025 diopter (inverse meters) is obtained ina planoconcave or planoconvex lens having a sagitta of microinches overa span of 0.5 inch.

Referring now to FIG. 1, let us assume that the line 2 represents such adistortion-analyzer trace. It would be seen that the line 2 has aportion, between the points 4 and 6, where the distortion sensed by thedistortion analyzer is relatively low, such that one windshield can besaved.

Referring now to FIG. 2, the curve 8 is of such nature that obviously nowindshield can be saved. In the curve 0, it will be understood that thepoints 10 and I2 indicate peaks that are indicative of distortion in theglass on the order of that produced by a microlens having a power ofabout 0.01 diopter, whereas in sheet glass of windshield quality, themaximum tolerable peak is on the order of 0.05 diopter and preferably isabout 0.0375 diopter or less.

Referring now to FIG. 3, the curve M has two good areas, separated by acentral region 16 wherein the distortion is excessive, and from a sampleof glass yielding such a distortionanalyzer trace, two windshield blankscan be saved.

Referring now to FIG. 4, the curve 18 has a region, extending from thepoint 20 to the point 22, from which a windshield blank can be saved,and it is located rather peculiarly, starting slightly to the left ofcenter of the sample and extending toward the right-hand edge butstopping substantially short of it.

it will be understood that the traces 2, 8, 14, and 18 refer to theentire width, as trimmed, of the sheet being produced, being on theorder of 85 to 110 inches. While it is desirable that thedistortion-analyzer equipment used be such as to scan such a length inone pass, equivalent results can be obtained, of course, withdistortion-analyzer equipment having a path length of, for example,about 22 inches, taking traces for the left, the left-center, theright-center, and the right portions of the sheet as separateoperations.

It is important to bear in mind that the distortion-analyzer readingsare taken in a direction transverse to the length of the ribbon of glassas it is drawn, since when this is done, maximal readings are ordinarilyobtained.

The method of the present invention involves scanning substantially theentire width of a piece of sheet glass that is being drawn with adistortion-analyzer apparatus that produces a record, e.g., a trace onan X-Y recorder, proportional to the various values, as one passes alongthe testing path, of the second derivative with respect to distancetraversed of the thickness of glass scanned, and then cutting from saidpiece at least one windshield blank, the windshield blank being takenfrom a portion of the piece wherein the said second derivative asindicated by the trace remains at less than a predetermined value, suchas 0.0375 diopter maximum.

ln practicing this method, it is preferable to have at least one, andpossibly more than one, distortion-analyzer apparatus capable ofscanning a path at least as long as 70 inches mounted in operativeassociation with a drawing machine, e.g., on the cutting floor. In oneway of practicing the method, the distortion-analyzer equipment is usedto produce a trace, and then a trained operator looks at the trace andthen sets the cutting equipment for making longitudinal cuts in theglass accordingly. Alternatively, the trained operator may merely mark,with chalk or paint or the like, the portion of glass that is to besaved, or the portion of glass that is to be discarded, with the cuttingof the windshield blanks then being performed by hand or by a cuttingmachine operator as a separate operation. It is also possible, ofcourse, to practice the method by using suitable automatic equipmentwhereby the cuts are made automatically in locations selected inaccordance with criteria built into the machine.

When the method of this invention is used, it becomes possible, with ahigh degree of reliability, to cut suitable windshield blanks fromvertically drawn sheet glass. Since tedious and time consuming handlingof the large pieces of glass is avoided, and since thedistortion-analyzer equipment operates reasonably rapidly, it becomespossible to test a considerably larger fraction of the product, therebyimproving quality control.

Although this invention may be used in producing windshield blanks andthe like from glass of any thickness that is produced in a verticaldrawing machine, the invention is of particular usefulness in the makingof windshield blanks that are 0.030 to 0.080 inch thick. Glass havingboth this quality and this thinness is not produced by the float orplate processes.

Referring now to FIG. 5, there is indicated schematically apparatus foruse in practicing the method of the invention. This comprises a drawingmachine 24, from which there issues a sheet or ribbon of glass G, whichis led to capping equipment 26, in which the glass is transverselyscored, snapped, and laid down. Operatively associated with the cappingequipment, there is cutting equipment 28 for making transverse cuts inthe glass at selected locations. A distortion analyzer 30 received by aline 32 from a sensor 34 visible light emanating from a source 36 andpassing through the glass G. The distortion analyzer produces, through aline 37 leading to an X-Y recorder 38 a trace 40 on the recorder 38 withthe trace 40 corresponding to the second derivative of the thickness ofthe glass and yielding a sensitive indication of its properties asrespects low-distortion characteristics. It is to be understood that thelight source 36 and the sensor 34 are mounted, by means not shown, formotion along a path length, corresponding substantially to the entirewidth of the ribbon of glass being tested. Vertical drawing machineshave never, prior to this invention, been provided with such equipment,and as a consequence, the prior art has lacked equipment for obtainingthe desired result, namely, the production from vertically drawn glassof thin low-distortion windshield blanks.

Although I have referred hereinabove to the use of an X-Y recorder, itwill be apparent to those skilled in the art that various equivalentmeans can be used to perform the same function-using magnetic tape,punched paper tape, or the programming of the memory of a computer ofeither the digital type or the analog type. The X-Y recorder ismentioned chiefly because it is a convenient and relatively inexpensivemeans for use in the practice of the invention.

When obtained, the thin windshield blanks are further processed in amanner familiar to those skilled in the art. For example, a windshieldblank produced in accordance with this invention may be assembledtogether with a suitable plastic interlayer and another windshield blankof float glass 0. l25 inch thick to form a finished windshield inaccordance with conventional practices.

I claim as my invention:

1. In a method of making Windshields from vertically drawn glass, theimprovement that comprises:

scanning substantially the entire width of the piece of the sheet beingdrawn with a distortion-analyzer apparatus that produces on a recordingmeans a record proportional to the second derivative with respect todistance traversed of the thickness of the glass scanned, saiddistortion-analyzer apparatus being of such sensitivity as to detectpeak thickness variations that have an apparent power on the order of0.025 diopter, and

cutting in accordance with the indications of said record from saidpiece at least one windshield blank, said windshield blank being takenfrom a portion of said piece wherein said derivative as indicated bysaid record remains at less than 0.0375 diopter.

2. The improvement defined in claim 1, characterized in that saidrecording means is an XY recorder and said record comprises a traceproduced by said X-Y recorder.

3. In combination with a vertical drawing machine from' which a sheet ofglass issues and capping equipment receiving said sheet of glass, adistortion analyzer for scanning in a one pass substantially the entirewidth of said sheet of glass and producing signals and a recording meansresponsive to said signals for producing a record indicative of thevariations in the second derivative of the thickness of the glass withrespect to distance traversed, said distortion analyzer being sensitiveto variations in said second derivative on the order of 0.025 diopter.

4. Apparatus as defined in claim 3, characterized in that said recordingmeans comprises an X-Y recorder and said record comprises a traceproduced by said X-Y recorder.

1. In a method of making windshields from vertically drawn glass, theimprovement that comprises: scanning substantially the entire width ofthe piece of the sheet being drawn with a distortion-analyzer apparatusthat produces on a recording means a record proportional to the secondderivative with respect to distance traversed of the thickness of theglass scanned, said distortion-analyzer apparatus being of suchsensitivity as to detect peak thickness variations that have an apparentpower on the order of 0.025 diopter, and cutting in accordance with theindications of said record from said piece at least one windshieldblank, said windshield blank being taken from a portion of said piecewherein said derivative as indicated by said record remains at less than0.0375 Diopter.
 2. The improvement defined in claim 1, characterized inthat said recording means is an X- Y recorder and said record comprisesa trace produced by said X- Y recorder.
 3. In combination with avertical drawing machine from which a sheet of glass issues and cappingequipment receiving said sheet of glass, a distortion analyzer forscanning in a one pass substantially the entire width of said sheet ofglass and producing signals and a recording means responsive to saidsignals for producing a record indicative of the variations in thesecond derivative of the thickness of the glass with respect to distancetraversed, said distortion analyzer being sensitive to variations insaid second derivative on the order of 0.025 diopter.
 4. Apparatus asdefined in claim 3, characterized in that said recording means comprisesan X- Y recorder and said record comprises a trace produced by said X- Yrecorder.